The present invention relates to a biomagnetism measurement device and a method of biomagnetism measurement which are suitable for measuring a magnetic field (for example, a magnetic field being caused by a nerve activity or myocardial activity of a heart) occurring from a portion to be measured of a living body (a patient to be inspected) by making use of a super conducting quantum interference device (hereinbelow abbreviated as SQUID) which serves as a highly sensitive magnetism sensor.
Since the SQUID which is developed in association with a growth of technology with regard to superconducting devices functions as a highly sensitive magnetism sensor, a technology which measures a magnetic field distribution caused by a living body making use of the SQUID and uses the same as medical diagnosis data is now being established in a medical measurement field.
FIG. 16 shows an arrangement diagram when such biomagnetism measurement device is applied for a cardio magnetism measurement system.
The cardio magnetism measurement is performed in a magnetically shielded room 1 so as not to be affected by environmental magnetic noises. A patient 2 to be inspected lies down on a bed 3, and is positioned close to and immediately below a bottom of a dewar (vessel) 4 so that a portion to be measured (a center position of a heart) meets with a center position of the dewar 4 (which includes magnetism sensors formed by integrating detection coils and the SQUIDs and is constituted by a cylindrical container filled with liquid He) supported by a gantry 5.
For He being evaporated, liquid He is continuously supplemented to a liquid He tank 6 by an automatic supply device 7 disposed outside the magnetically shielded room 1.
Outputs of the magnetism sensors are inputted to an FLL circuit 8 wherein voltage outputs proportional to the detected magnetic field intensities are obtained. The output voltages are amplified and of which frequency band are selected via an amplifier and filter circuit 9, and are taken in by a computer 10 after being A/D converted, wherein signal processing is performed and the processed data are outputted therefrom.
A dewar 4 for the biomagnetism measurement, for example, as disclosed in G. L. Romani, et al., Rev. Sci. Instrom, 53. pp. 1815-1845(1982), is configurated in a cylindrical shape or a combination of cylinders of different diameters and is disposed vertically because of easy production from its structural point of view.
Further, in a system for measuring a cardio magnetism most of the bottom faces of such cylindrical shaped dewars are configurated in flat, because a chest wall of a living body is nearly flat. In case of cardio magnetism measurement, after a patient to be inspected lay on the patient""s back on the bed 3 which is constituted to be movable freely (permitted position adjustment) in backward and forward, right and left and upward and downward with respect to the dewar 4, it was necessary to meet the heart portion (center position of the heart) in the chest wall area of the patient 2 to be inspected with the center position of the bottom face of the dewar 4 and to come close thereto by adjusting respective movable portions in the bed 3.
However, if the measurement portion of the patient to be measured touches the bottom face of the dewar 4 which causes noises, therefore, it is necessary to place the measurement portion away therefrom to some extent, however, if the measurement portion is placed away excessively, the sensitivity of the sensors reduces, therefore, a positioning operation has to be repeated many times for determining an optimum position visually.
FIG. 17 shows a conventional common method of positioning a measurement portion with respect to a dewar 4.
In the conventional cardio magnetism measurement device the bed 3 for placing the patient 2 to be inspected thereon is disposed on a traveling stand 12 which is movable in back and forth direction along back and forth transferring use trails 11 via an elevation means 13 and a right and left direction moving means 14.
The traveling stand 12 is either manually driven or electrically driven by a motor, and moves in the back and forth direction on the back and forth transferring use rails 11. At the retreated state of the traveling stand 12, the traveling stand 12 positions the bed 3 at a measurement preparation position, in that a position away from the dewar 4, where the patient 2 gets on and off the bed 3 as well as the posture of the patient 2 is corrected for the measurement, and at the advanced state the traveling stand 12 positions the bed 3 at a measurement position where the patient 2 is placed immediately under the dewar 4.
The elevation means 13 is disposed between the traveling stand 12 and the right and left direction moving means 14. The elevation means 13 elevates and deelevates the right and left direction moving means 14 (the bed 3) by a hydraulic expansion and contraction means constituted by a hydraulic cylinder and piston. Through manipulation of an elevation use hydraulic pump handle 17 pressurized oil is supplied in the hydraulic cylinder to elevate the right and left direction moving means 14, and when pushing a relief valve 18, the pressure oil in the hydraulic cylinder is discharged to deelevate the right and left direction moving means 14.
The right and left direction movement means 14 supports the bed 3 in such a manner to permit the bed 3 to move in right and left direction. When rotating a right and left transferring handle 16, the bed 3 is caused to move in right or left direction through a combination of a pinion and rack or a ball screw mechanism.
In order to place the patient 2 in a measurable condition in which the chest (the heart portion) of the patient 2 comes close to and immediately below the center of the bottom portion of the bewar 4, at first the traveling stand 12 is retreated along the back and forth direction transferring rails 11 to move the bed 3 to the measurement preparation position, thereafter, the patient 2 is laid on the bed 3 on the patient""s back and the posture thereof is corrected. At this instance, the elevation means 14 deelevates the bed 3 to the lowest position or a predetermined height suitable for getting on and off the bed 3.
Thereafter, the traveling stand 12 is advanced along the back and forth transferring use rails 11 and moves the bed 3 to the measurement position under the dewar 4 to perform position matching of the heart center of the patient 2 with the bottom center of the dewar 4.
In order to match the heart center of the patient 2 with the bottom center of the dewar 4, it is necessary to perform the matching while observing a pin point marking of the heart of the patient 2 (usually the heart center position is estimated which is shifted by predetermined distances in X and Y axis directions from the position of a xiphoid process which is determined in advance through palpation, and this estimated position is determined as the pin point marking position). With this positioning method, because of the narrow space between the patient 2 and the dewar 4, the chest of the patient 2 is hidden behind the dewar 4 which causes insufficient confirmation of the positions of the dewar 4 and the pin point marking. For this reason, the setting is conventionally performed under insufficient matching, therefore, correlation between the sensor positions in the dewars 4 and the measurement portion is hardly taken which causes the position matching difficult. In particular, when many number (multi-channels) of magnetism sensors are arranged in the dewar 4, it was difficult to correlate the magnetism sensors for respective channels with the measurement portion.
The correlation between the magnetism sensors and the measurement portion is very important in data processing (position calibration) for the heart diagnosis. Further, it is possible to use the cardio magnetism measurement data in such a manner to superpose the same over an X ray image of the chest of the patient 2 to perform diagnosis such as to specify an abnormal portion of the heart, in such instance, the cardio magnetism measurement data (biomagnetic flux distribution) are superposed over the X ray image using the pin point marking as a guide, therefore, if the correlation between the magnetism sensors and the measurement portion can not be taken sufficiently as has been explained above, troubles are caused.
In order to countermeasure these problems, a biomagnetism measurement device having multi channel magnetism sensors, for example, as disclosed in JP-A-3-244433, is proposed in which a plurality of optical fibers serving as a collimator irradiating the measurement portion of the patient are prepared, these respective optical fibers are corresponded in one to one relation to respective pick-up coils (magnetism detection coils) incorporated in the dewar and the positioning between the measurement portion and the dewar is performed by using the lights (light spots) irradiated from the respective optical fibers as a guide. Further, in this conventional art the following position matching method between the dewar and the measurement portion is proposed, in that the collimator and the dewar are constituted separately and are disposed with a predetermined distance L, and when performing a measurement, at first a patient is laid on a moving stand (bed), then the moving stand is moved to a position opposing the collimator to set a position to be measured of the patient by the collimator, finally, the moving stand is moved (parallel displacement) by the distance L to a position opposing to the dewar.
However, even with the above explained method in which the lighting collimator and the dewar are disposed in separate positions with distance L, and the measurement portion and the position of light spots are matched in advance at a position remote from the dewar, thereafter, the patient is displaced by the distance L toward the dewar, when applying the multi-channel method, light sources and optical fibers each corresponding to the respective magnetism sensors have to be prepared, and further, when the body axis of the patient is inclined with respect to a coordinate axis of the dewar, it was impossible to detect the inclination with the light spots (when the measurement portion is specified under a body axis inclined condition, the position matching accuracy between the coordinate positions of the measurement position and these of the magnetism sensors is caused to vary and errors with respect to recognition of the respective positions of the measurement portion are resulted).
Further, a cardio magnetism measurement device as disclosed in JP-A-2-180244 proposes that in order to match a light beam (a light spot) from a light source with an index such as a marker attached to a patient, a top board of a bed on which the patient is laid is displaced, thereafter, the light source is retreated and at the very position where the light source was located a SQUID sensor is fixed.
Still further, JP(U)-A-57-13006 discloses still another conventional art in which a similar positioning is performed by making use of a like collimator.
However, among the conventional art in which the positioning use light spots are irradiated to the measurement portion of the patient in order to correlate between the magnetism sensors and the measurement portion, in the arrangement where the light collimator is provided at the bottom face of the dewar, when the dewar is caused to approach the patient, the light spots irradiated onto the patient can not be observed because the dewar blocks the visual field, therefore, the approaching distance of the dewar and the magnetism sensors is limited by itself.
After position matching between the heart center of the patient 2 and the bottom center of the dewar 4, through elevation of the bed 3 by manipulating the elevation use hydraulic pump handle 17, the patient 2 is, while observing visually, caused to approach to the bottom of the dewar 4.
Since the elevation amount of the bed 3 immediately below the dewar 4 varies depending on the body shape of the patient 2, the elevation amount has to be varied to a proper amount at every measurement, therefore, when the bed is excessively elevated, the patient 2 may be heavily caught between the dewar 4 and the bed 3 which causes problems with regard to manipulability and safety.
Further, when the elevation amount is short, an excessively large gap is set between the patient 2 and the bottom face of the dewar 4 which causes a problem of reducing measurement sensitivity.
Moreover, when the chest of the patient 2 approaches the dewar 4, opposing portions of the chest and the bottom face of the dewar 4 are hidden behind the dewar 4 which makes a visual observation of the degree of approaching of the bottom face of the dewar 4 difficult, resultantly, an operator has to perform the setting by the sixth sense which incurs a substantial burden on the operator.
The present invention is developed in view of the above problems, and an object of the present invention is to be provide a biomagnetism measurement device and a method of positioning a patient in the biomagnetism measurement device which permit an accurate and easy positioning between a dewar (magnetism sensors) and a measurement portion of the patient.
A present invention, which achieves the above object, is, in principle, constituted in the following manner.
According to a first aspect of the present invention, a biomagnetism measurement device comprising magnetism sensors including SQUIDs and a dewar which incorporates the magnetism sensors and is filled with a coolant so as to maintain the same in a super conducting state, is characterized in that the biomagnetism measurement device further comprises a light projecting means which projects cross shaped beam patterns used for positioning a measurement portion of a patient.
With the above construction, when performing a biomagnetism measurement, the positioning use cross shaped beam patterns are irradiate onto an inspection use patient laying apparatus (for example, an inspection use bed or chair), and a position matching is performed so that the crossing point of the beam patterns meets with a mark (pin point marking) at the center of the measurement portion of the patient (for example, an estimated position of the heart center). Further, thereafter, the center of the measurement portion is finally matched with the center of the dewar such as by performing position matching so that the center of the dewar meets with the crossing point of the cross shaped beam patterns on the patient laying apparatus and by relatively displaying the patient laying apparatus by a predetermined distance with respect to the dewar.
According to the present invention, the cross shaped beam patterns can be used as X and Y coordinate axes while assuming the crossing point as the origin, therefore, the crossing point of the cross shaped beam patterns is corresponded to the center of the measurement portion and the center of the dewar, and the positional relationship between the measurement portion and the multi channel magnetism sensors is correlated by making use of the X and Y coordinated axes. Different from an X ray CT and an MR imaging device, in a biomagnetism measurement device, the measured data do not contain any positional data of the measurement portion, therefore, the position matching between the measurement portion and the magnetism sensors is a very important technology. Further, when setting one of two axes of the cross shaped beam patterns, for example, Y axis in the body axis direction of the patient, and if the body axis is inclined with respect to the Y axis beam pattern, the inspection figure (inclination) of the patient can be corrected so that the body axis thereof meets with the Y axis beam pattern, thereby, a biomagnetism measurement can be performed with a correct posture of the patient (in other words, by correcting offsetting between the X axis and Y axis coordinate system of the dewar and that of the measurement portion of the patient).
A second aspect of the present invention, which is an application invention of the above first aspect invention, primarily comprises the magnetism sensors, the dewar and the light projecting means of the cross shaped beam patterns like the first aspect invention and in addition comprises marks which are used for setting X axis and Y axis coordinate system on the measurement portion of the patient.
These marks are attached in total at three points on the body of the patient, one representing the origin of the coordinate system and other two are respectively provided at any point on X axis and Y axis, and when a position matching between the patient (patient laying apparatus) and the dewar is performed so that these three points position on the cross shaped beam patterns, the correlation between the measurement portion of the patient and the dewar can be determined while eliminating a possible coordinate axes offsetting as much as possible.
A third aspect of the present invention which is also an application invention of the first aspect invention, is characterized in that the third aspect of the present invention primarily comprises a light projecting means which projects cross shaped beam patterns used for positioning the measurement portion of the patient on a measurement preparation position outside a position immediately below the dewar, wherein relative positions between a crossing point of the cross shaped beam patterns irradiated on the measurement preparation position outside the position immediately below the dewar and a position which is on an extension line passing the center of the dewar representing a measurement position immediately below the dewar are determined in advance, and further comprises a displacing means having a displacement amount control mechanism which effects a constant amount of transfer between the relative positions for at least one of the patient laying apparatus laying the patient thereon and the dewar.
According to the present invention, the cross shaped beam patterns are irradiated to the measurement preparation position which is never obstructed by the dewar and therein the patient laying apparatus is aligned and adjusted so that the measurement portion will meet with the crossing point of the cross shaped beam patterns, thereafter, it is possible to position the patient at the position immediately below the dewar by transferring the patient laying apparatus by a constant amount and at the same time the center of the measurement portion of the patient automatically meets with the center of the dewar.
A biomagnetism measurement device according to a fourth aspect of the present invention, which is also an application invention of the first aspect invention, primarily comprises the magnetism sensors and the dewar, is characterized in that the biomagnetism measurement device further comprises, a displacement means which freely transfers the patient laying apparatus laying the patient thereon for inspection between a measurement position immediately below the dewar and a measurement preparation position outside the position immediately below the dewar, and a light projecting means which projects cross shaped beam patterns used for positioning the measurement portion of the patient, and a first dewar mark used for performing position matching between X axis of the beam pattern and X axis of the dewar and a second dewar mark used for performing position matching between Y axis of the beam pattern and Y axis of the dewar are provided at the side face of the dewar, the light projecting means includes a first projector of which beam spreads in one direction and a second projector of which beam spread in a direction crossing the beam from the first projector, the first projector is disposed in such a manner that the beam spreading direction projected therefrom is in parallel with the free transferring direction of the patient laying apparatus and the beam covers the position outside the position immediately below the dewar and the first dewar center mark provided at the side face of the dewar, and the second projector is mounted and disposed on said displacement means in such a manner that the beam spreading direction projected therefrom is to be perpendicular to the free transferring direction of the displacement means.
According to the present invention, the cross shaped beam patterns are irradiated to the measurement preparation position which is not obstructed by the dewar by making use of the first and second projectors and therein a position matching is performed so that the measurement portion of the patient comes to the crossing point of the cross shaped beam patterns, thereafter, the patient laying apparatus is transferred in parallel with the beam spreading direction from the first projector until a position where the beam from the second projector which displaces together with the patient laying apparatus covers the second dewar mark provided on the side face of the dewar, thereby, a position matching between the crossing point of the cross shaped beam patterns (the center of the measurement portion) and the center of the dewar even at the measurement position immediately below the dewar is substantially facilitated.
A fifth aspect of the present invention relates to a positioning method making use of the above second and third aspects of the present invention and primarily comprises the following steps, in that when measuring magnetism of the measurement portion of the patient by making use of the dewar which maintains magnetism sensors including SQUIDs under a ultra low temperature, a patient laying apparatus laying a patient for inspection is located at a measurement preparation position outside a position immediately below the dewar, at the measurement preparation position outside the position immediately below the dewar the patient is laid on the patient laying apparatus under a condition of inspection figure, marks are attached at three points on the body of the patient so as to set X and Y coordinate axes on the measurement portion, further, cross shaped beam patterns are projected at the measurement preparation position outside the position immediately below the dewar, the position of the patient laying apparatus is adjusted so that the marks at the three points position on the cross shaped beam patterns, thereafter, the patient laying apparatus is transferred by a constant amount to a position immediately below the dewar, and the constant transferring amount is determined by the distance between the crossing point of the cross shaped beam patterns in the measurement preparation position and an extension line passing through the center of the dewar in the measurement position immediately below the dewar.
According to the present invention, only with the irradiation of the cross shaped beam patterns in the measurement preparation position outside the position immediately below the dewar and with the constant amount of transferring of the patient laying apparatus, the position matching between the measurement portion and the center of the dewar is realized, and, in addition, through introduction of the position matching method between the marks at the three points attached to the measurement portion of the patient and the cross shaped beam patterns, a positioning can be realized which further accurately determines the correlation of X and Y coordinate axes of the measurement portion and the dewar.
A sixth aspect of the present invention relates to a positioning method making use of the above second and fourth aspects of the present invention and primarily comprises the following steps, in that when measuring magnetism of the measurement portion of the patient by making use of the dewar which maintains magnetism sensors including SQUIDs under a ultra low temperature, a patient laying apparatus laying a patient for inspection is located via a displacement means at a measurement preparation position outside a position immediately below the dewar, at the measurement preparation position outside the position immediately below the dewar the patient is laid on the patient laying apparatus under a condition of inspection figure, marks are attached at three points on the measurement portion in advance so as to set X and Y coordinate axes, on the other hand, a first dewar mark used for performing position matching between X axis of the beam pattern and X axis of the dewar and a second dewar mark used for performing position matching between Y axis of the beam pattern and Y axis of the dewar are provided at the side face of the dewar, further two projectors are prepared which perform separate irradiation, among the two projectors the first projector is disposed in such a manner that the beam spreading direction projected therefrom is in parallel with the free transferring direction of the patient laying apparatus and the beam covers the position outside the position immediately below the dewar and the first dewar center mark provided at the side face of the dewar, and the second projector is mounted on the displacement means in such a manner that the beam spreading direction projected therefrom is to be perpendicular to the transferring direction of the patient laying apparatus, cross shaped beam patterns formed by making use of the first and second projector are projected at the position outside the position immediately below the dewar and the position of the patient laying apparatus is adjusted so that the marks at the three points attached to the patient locate on the cross shaped beam patterns, thereafter, the patient laying apparatus is transferred to the position immediately below the dewar by making use of the displacement means, and the transferring of the patient laying apparatus is effected until the beam projected from the second projector which displaces together with the patient laying apparatus meets with the second dewar mark.
According to the present invention, likely, only with the irradiation of the cross shaped beam patterns in the measurement preparation position outside the position immediately below the dewar and with the transferring of the patient laying apparatus (not limited to the constant amount of transferring), the position matching between the measurement portion and the center of the dewar is realized, and, in addition, through introduction of the position matching method between the marks at the three points attached to the measurement portion of the patient and the cross shaped beam patterns, a positioning can be realized which further accurately determines the correlation of X and Y coordinate axes of the measurement portion and the dewar.
Further, when the biomagnetism distribution data obtained according to the respective aspects of the present invention are superposed, for example, over a pseudo cardio pattern image or an actual heart image (X ray image), a positional correlation between the respective sensors and the respective portions of the heart can be determined, thereby, correlations between extraordinary output data of respective sensors in the dewar and portions of coronary abnormality and cardiac muscle abnormality of the heart are, for example, clarified which permits diagnosis on abnormal portions of the heart.
A biomagnetism measurement device according to a seventh aspect of the present invention comprises a dewar incorporating magnetism sensors and a patient laying means laying a patient thereon, is characterized in that the biomagnetism measurement device further comprises a gap detecting means which outputs a light beam so as to pass between a measurement preparation position outside a position immediately below the dewar and a measurement position immediately below the dewar while maintaining a slight distance with respect to the bottom face of the dewar and so as to detect interruption of the light beam due to approach of the patient to the bottom face of the dewar, wherein adjustment of a gap between the patient and the bottom face of the dewar is performed under a safe condition at the measurement preparation position and after adjusting the patient and the bottom face of the dewar at a predetermined gap, the patient is displaced to the measurement position, the details of the present invention will be explained later with reference to FIGS. 11 through 15.
Further, the seventh aspect of the present invention can be practice together with the first through sixth aspects of the present invention.